1. Field of the Invention
The present invention relates inter alia to a micromachined package useful, for example, for high frequency circuits and also to a method for directly interconnecting silicon packaged circuits.
2. Description of Related Art
The integration of Monolithic Microwave Integrated Circuits (MMIC""s) into high frequency communication systems and devices has increased the need for a low cost packaging system that can be mass produced. Conventional packing techniques are inadequate for high frequency devices, such as the MMIC, because the package fails to adequately transmit the signal thus resulting in a loss with every transition.
Traditionally, integrated circuits (IC) formed on a semiconductor chip are packaged by enclosing the chip within a plastic or ceramic casing and then attaching wire bonds between the pads of the chip and the package leads which can be soldered to a circuit board. This technique is acceptable for low frequency devices. When applied to high frequency devices however, the millimeter components corresponding to the high frequency components of the signal exhibit odd behavior because the standard package can not carry the high frequency signal. These losses and the erratic signal behavior occur as a result of the internal structure of the package and the signal transitioning from one package down to the circuit board and back up into another package.
In addition to the need for a low cost packaging with low signal loss, a solution is also needed to solve other assembly problems. For example, assembling a module having multiple chips using either the traditionally packaged chip or bare die assembly requires extensive time sacrifices and numerous prototype iterations before a final design is produced. Forming modules using conventionally packaged chips mandates numerous hours of design and tedious wire bonding that often results in mistakes, thus requiring the module to be either scrapped or reassembled. The long time needed to produce a module greatly increases the manufacturing cost. Accordingly, there is an immense need to eliminate multiple prototype iterations and the long time needed to produce packaged integrated circuits useful in high frequency applications, by creating a low cost package and packaging method, with interconnection capabilities between packaged integrated circuits, thus enabling a module to be assembled with exact precision in a short period of time.
The present invention solves the above disclosed and other problems by introducing a low cost packaging technology for high frequency devices wherein individual packages can be directly attached to one another and then surface mounted as a unit to form a module of multiple integrated circuits on multiple chips. As will be described in detail below, one or more chips with integrated circuits can be mounted on a substrate of high resistivity material with metal conductors patterned on the substrate. A means is provided for coupling the desired wave signals from one side of the substrate to the other side through the substrate.
Additionally, the package has the capability to be interconnected with other packages. The package may be shaped as either a plug or a socket or the package may have both the plug and socket capability. The packages are then directly attachable to one another.
Direct package-to-package attachment provides significant performance advantages over circuit-board-based interconnections. By directly attaching the packages to one another, the signal is directly transmitted between packages. The interconnection therefore solves the signal loss problem experienced using traditional packaging techniques by preventing the signal from repeatedly passing up and back between the packages and circuit board. The technology of the invention greatly simplifies the RF design since the transmission line maintains essentially a constant cross-section until immediately before reaching the MMIC.
The interconnection packaging technology of this invention offers immense commercial capabilities since the interconnection of packages enables various modules of multiple packages to be assembled quickly. Thus, integrated circuits can be packaged in packages of the invention and multiple packaged circuits can be quickly and easily joined together to form selected circuit combinations, such as amplifiers easily connected with modulators and the like. The electrical characteristics of the packages being very similar assures not only low losses between packages but repeatability of circuit characteristics among the supply of packaged circuits. Thus, the prepackaged chips are standardized, thereby guaranteeing precise circuit characteristics as a result of the constant circuit environment and connections. Using plural prepackaged chips of the invention, a designer can create a module by selecting the appropriate prepackaged chips and directly coupling the packages to one another (i.e.: a plug and play concept). This ability allows modules to be created in a rapid and precise environment, thereby eliminating the traditional prototype to final design procedure that required weeks to perfect.
In one aspect of the invention, a package having interconnection capabilities uses a plug-and-socket approach. Two substrates made, for example, from silicon or ceramic or other suitable material for micromachining, are fabricated to include at least one of a male (plug) and female (socket) formation. The plug may be trapezoidal in cross section while the socket may have a dovetail-joint-like aperture. The plug is accepted by the socket thereby directly attaching one IC package to another. The two packages would be locked together when the plug portion is fitted to the socket portion. Of course the plug/socket combination s not limited to the trapezoidal/dovetail cross section or even to the male/female type connector arrangement. The invention envisions any type of direct, stable intersection between packages using connector portions integral with the respective substrates of interconnected packages. These connector portions further include respective contact portions for electrical signed flow.
In another aspect of the present invention, the package""s direct attachment configuration may comprise a cross type layout wherein two or more connectors, for example, four plugs/sockets are provided with one plug or socket extending from a respective edge of the package. Such a configuration allows multiple packages to be coupled to a single package of the invention. Any module configuration that enables two or more packages to be coupled together are within the scope of this invention.
In yet another aspect of the present invention, two packages of the invention are held together by a flexible spring formed integral with the package substrate. The spring applies a compressive force when the two packages are mated, thus bringing the respective contact portions are placed in electrical contact. The spring may create a frictional force keeping the components coupled together. The spring edges may be tapered to ease insertion into a spring seat on an adjoining package, consequently providing a positive lock when the packages are fully joined together.
In still another aspect of the present invention, two packaged MMIC""s are directly coupled via a double plug configuration. The double plug configuration utilizes one plug for providing coarse alignment, which may be termed a guide plug, while the second plug carries the signal and may be termed a signal plug. The signal plug provides the spring binding force. In this configuration, the guide plug restricts the signal plug""s range of travel so that the movement of the signal plug in the socket does not exceed the maximum excursion of the spring, regardless of the position and direction in which the packages are brought together.
In still another aspect of the present invention, a package is fabricated to provide full encapsulation of a semiconductor chip. The semiconductor chip is sealed within a cavity formed between two or more patterned substrates. Alternatively, the semiconductor chip is mounted between two or more patterned substrates, a window may also be formed in at least one of the substrates so that the chip can be viewed through the aperture.
In another aspect of the present invention, MMICs or other integrated circuits are mounted on a package substrate prior to bonding step whereby a second package substrate is bonded to the first package substrate carrying the MMIC. The first substrate is then bonded to the second substrate thereby simultaneously sealing the MMIC between the substrates. A prepackaged semiconductor device that can be mass-produced and coupled to other devices to form a module.
In another aspect of the present invention, the integrated circuit is not mounted before wafer bonding. The IC packages are not completely sealed. Instead, the package has a window etched above the site where the IC will be mounted. In one aspect, two substrates may be bound together and with a window an forming empty package.
Many packages may be formed simultaneously on wafers such as a silicon wafer. On a first wafer is formed multiple first substrates at respective die positions in the wafer. On a second wafer may be formed multiple second substrates at respective positions. The wafer can be aligned and bonded to each other thereafter the bonded wafers can be diced apart. In one embodiment, ICs can be mounted between the two substrates before the wafers are diced apart. In another embodiment no ICs are mounted before the dicing operation and after the dicing the individual packages formed by each die can be sold as an empty package. A user could then mount an IC such as an MMIC through a window located on the package. The user could then wire bond the connections and seal the packages with a cap, such as a metal cap.
Objects, features and advantages of this invention is to provide a low cost mass producible package and packaging system that can be used with high frequency devices. An aspect of the packaging system of the present invention is to enable the packages and the chips mounted therein to be interconnected via a direct attachment to one another thereby reducing loss. The present invention also eliminates the multiple prototype cycle inherent in traditional module design by providing a technology wherein a module may be immediately created by assembling prepackaged IC""s with interconnecting capabilities.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.